The White House said the international community would not recognise a referendum carried out ‘under threats of violence and intimidation’ and vowed to punish Russia unless it withdrew its forces from Crimea.

There was also strong condemnation from European leaders who will meet tomorrow in Brussels to discuss whether to push ahead with sanctions.

But Russian president Vladimir Putin dismissed the criticisms, saying the vote was free and fair.

In Kiev, interim Ukrainian prime minister Arseny Yatseniuk threatened dire consequences for the Crimean politicians who had pushed for the vote.

‘We will bring them to justice. The ground will burn under their feet,’ he told a cabinet meeting.

In Simferopol, Crimea’s capital, veterinary nurse Svetlana Vasilyeva said: ‘I have voted for Russia. We are one family and we want to live with our brothers.’

Anger as troops take first steps over border

Russian forces have crossed into mainland Ukraine for the first time since the start of the crisis sparking outrage in Kiev ahead of today’s Crimea referendum.

Troops backed by helicopter gunships and armoured vehicles seized control of a gas plant near the village of Strilkove.

They took temporary control of the village before retreating to the plant. Ukrainian soldiers responded by digging trenches and putting up barricades nearby.

‘We will not let them advance further into Ukrainian territory,’ said Serhiy Kuz, commander of a paratrooper battalion.

Kiev also announced plans to arm and train 20,000 members of a newly created National Guard to ‘defend the nation’.